Nonaqueous electrolyte secondary battery and method of manufacturing the same

ABSTRACT

Provided is a nonaqueous electrolyte secondary battery in which a flat wound electrode body, a nonaqueous electrolytic solution, and an insulating film are accommodated in a quadrilateral battery case. The insulating film is formed into a bag shape corresponding to a shape of the electrode body and is arranged between an inner wall of the battery case and the electrode body. An entire surface of a bottom-side R portion of two R portions of the electrode body, which faces a bottom surface of the battery case, and an inside of the bag-shaped insulating film, which faces the bottom-side R portion of the electrode body, are joined to each other.

INCORPORATION BY REFERENCE

This application is a divisional application of U.S. application Ser.No. 14/932,223 filed Nov. 4, 2015, which claims priority to JapanesePatent Application No. 2014-224725 filed on Nov. 4, 2014, the contentsof all of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a battery (nonaqueous electrolytesecondary battery) including a nonaqueous electrolytic solution and amethod of manufacturing the same.

2. Description of Related Art

The importance of nonaqueous electrolyte secondary batteries such as alithium ion secondary battery has increased as a power supply, forexample, a vehicle-mounted power supply or a power supply for a PC, aportable device, or the like. In particular, a lithium ion secondarybattery is preferably used as a vehicle-mounted power supply with highoutput because it is light-weight and has high energy density. As astructure of such a battery, a battery structure is known including anonaqueous electrolytic solution and a wound electrode body in which asheet-shaped positive electrode and a sheet-shaped negative electrodeare laminated and wound together with a separator. From the viewpoint ofobtaining high physical strength, a metal case is used as a batterycase. In this case, typically, an electrode body is covered with aninsulating film to insulate the battery case and the electrode body fromeach other. For example, Japanese Patent Application Publication No.2006-278245 (JP 2006-278245 A) and Japanese Patent ApplicationPublication No. 2009-026704 (JP 2009-026704 A) discloses batteriesincluding an electrode body and a battery case, in which an insulatingfilm is arranged between the electrode body and the battery case.

In the nonaqueous electrolyte secondary battery having theabove-described configuration, a space between the positive electrodeand the negative electrode (that is, an internal space of an electrodebody) is filled with an appropriate amount of a nonaqueous electrolyticsolution to realize the smooth movement of charge carriers between theelectrodes. Therefore, when the liquid volume of the nonaqueouselectrolytic solution held in (impregnated into) the electrode body islower than a necessary volume (that is, when liquid shortage occurs),charge-discharge performance may deteriorate. For example, the shortageof the nonaqueous electrolytic solution may cause a decrease in cyclecharacteristics (a decrease in cycle characteristics caused by high-ratecharging and discharging). Therefore, when the nonaqueous electrolytesecondary battery is used for an application in which charging anddischarging are repeated at high input and output densities (forexample, a vehicle-mounted battery in which high-rate charging anddischarging is repeated) or for an application in which it is requiredthat high battery performance can be exhibited for a long period of time(an application in which a long lifetime is required; for example, avehicle-mounted battery which is generally used for 10 years or longer),it is strongly desired to prevent the shortage of the nonaqueouselectrolytic solution.

In a nonaqueous electrolyte secondary battery in which a wound electrodebody having a flat shape in a section perpendicular to a winding axis isaccommodated in a quadrilateral battery case, a gap may be formedbetween a bottom-side R portion of the wound electrode body and a cornerportion of the bottom of the battery case. From the viewpoint of impactresistance, the electrode body may be arranged in the battery case suchthat the top of the bottom-side R portion of the electrode body isseparated from the bottom of the battery case. However, even with theabove-described configuration, a gap is formed between the bottom-side Rportion of the electrode body and the bottom of the battery case. Thenonaqueous electrolytic solution held in this gap is not used for a cellreaction (movement of charge carriers between the electrodes). Thenonaqueous electrolytic solution impregnated into the electrode bodyduring battery construction may flow out from the electrode body duringuse of the battery. For example, electrode active materials contained inthe positive electrode and the negative electrode may expand andcontract due to repeated charging and discharging (in particular,high-rate charging and discharging) which forces the nonaqueouselectrolytic solution outward from the inside of the electrode body.When the nonaqueous electrolytic solution flowing out from the electrodebody is held in a gap between the bottom-side R portion of the woundelectrode body and the bottom of the battery case, the amount of thenonaqueous electrolytic solution held in (impregnated into) theelectrode body may be insufficient.

SUMMARY OF THE INVENTION

The invention provides a nonaqueous electrolyte secondary battery inwhich cycle characteristics (in particular, high-rate cyclecharacteristics) are superior by improving performance of holding anonaqueous electrolytic solution in an electrode body (hereinafter, alsoreferred to as “liquid holding ability of an electrode body)”.

According to a first aspect of the invention, there is provided anonaqueous electrolyte secondary battery including: a flat woundelectrode body; a nonaqueous electrolytic solution; a quadrilateralbattery case that accommodates the electrode body and the nonaqueouselectrolytic solution; and an insulating film that electricallyinsulates the electrode body and the battery case from each other. Theinsulating film is formed into a bag shape corresponding to a shape ofthe electrode body and is arranged between an inner wall of the batterycase and the electrode body. The wound electrode body is formed bymaking an elongated positive electrode and an elongated negativeelectrode overlap each other with an elongated separator interposedtherebetween to obtain a laminate and winding the laminate in alongitudinal direction of the elongated positive electrode and theelongated negative electrode. The wound electrode body has two Rportions and a flat portion, the two R portions have a curved surfaceand are formed in opposite end portions in a longitudinal direction of asection perpendicular to a winding axis, and the flat portion is acenter portion in the longitudinal direction of the section and isinterposed between the two R portions. An entire surface of thebottom-side R portion of the two R portions of the electrode body, whichfaces a bottom surface of the battery case, and an inside of thebag-shaped insulating film, which faces the bottom-side R portion of theelectrode body were joined to each other.

According to the above-described configuration, the inside of thebag-shaped insulating film which faces the bottom-side R portion of theelectrode body is joined to the entire surface of the bottom-side Rportion of the electrode body. Therefore, the nonaqueous electrolyticsolution is not likely to be held in a gap between the bottom-side Rportion of the electrode body and the bottom of the battery case. Thus,even when the nonaqueous electrolytic solution impregnated into theelectrode body flows out from the electrode body, the nonaqueouselectrolytic solution can be easily supplied into the electrode bodyagain. In other words, according to the above-described configuration,the liquid holding ability of the electrode body is improved, and theliquid shortage in the electrode body can be prevented. That is,according to the invention, a nonaqueous electrolyte secondary batteryhaving superior cycle characteristics (in particular, high-rate cyclecharacteristics) can be provided. The nonaqueous electrolytic solutionsupplied into the battery case can be supplied (impregnated) into theelectrode body without being held in a gap between the bottom-side Rportion of the electrode body and the bottom of the battery case.Therefore, the amount of the nonaqueous electrolytic solution (inparticular, a nonaqueous solvent constituting the nonaqueouselectrolytic solution) used can be reduced. According to theabove-described configuration, since the insulating film is joined tothe electrode body, the insulating film is not likely to deviate from apredetermined position. For example, the following situations can beprevented including: a position deviation of the insulating film whichmay occur when the electrode body accommodated in the insulating film isinserted into the battery case; and a situation in which the insulatingfilm falls to the bottom of the battery case due to gravity after theelectrode body accommodated in the insulating film is accommodated inthe battery case. That is, an electrode or a conductive member(typically, a positive electrode current collector terminal, a negativeelectrode current collector terminal, or the like) can be prevented frombeing exposed due to the position deviation of the insulating film. As aresult, internal short-circuiting, which may occur due to contactbetween the battery case and the exposed conductive member or the like,can be prevented. According to the above-described configuration, poorwelding, which may occur by inserting the positionally deviatedinsulating film into a welded portion of the battery case (between acase body and a lid of the battery case), can be prevented.

The entire surface of the bottom-side R portion of the electrode bodyand the inside of the bag-shaped insulating film which faces thebottom-side R portion of the electrode body may be joined to each otherthrough welding of the insulating film. Alternatively, the entiresurface of the bottom-side R portion of the electrode body and theinside of the bag-shaped insulating film which faces the bottom-side Rportion of the electrode body may be joined to each other through anadhesive member or a bonding member. According to the above-describedconfiguration, the entire surface of the bottom-side R portion of theelectrode body and the insulating film which faces the bottom-side Rportion of the electrode body can be reliably joined to each other.

According to a second aspect of the invention, there is provided amethod of manufacturing a nonaqueous electrolyte secondary battery, thenonaqueous electrolyte secondary battery including a flat woundelectrode body, a quadrilateral battery case that accommodates theelectrode body and a nonaqueous electrolytic solution, and an insulatingfilm that electrically insulates the electrode body and the battery casefrom each other.

This manufacturing method includes:

(i) a step of constructing the flat wound electrode body by making anelongated positive electrode and an elongated negative electrode overlapeach other with an elongated separator interposed therebetween to obtaina laminate and winding the laminate in a longitudinal direction of theelongated positive electrode and the elongated negative electrode, inwhich the electrode body has two R portions and a flat portion, the twoR portions have a curved surface and are formed in opposite end portionsin a longitudinal direction of a section perpendicular to a windingaxis, and the flat portion is a center portion in the longitudinaldirection of the section and is interposed between the two R portions;

(ii) a step of accommodating the constructed electrode body in abag-shaped insulating film and joining an entire surface of one of thetwo R portions of the electrode body and an inside of the bag-shapedinsulating film, which faces the R portion of the electrode body, toeach other;

(iii) a step of inserting the electrode body, to which the insulatingfilm is joined, into the battery case such that one of the two Rportions of the electrode body, to which the insulating film is joined,faces a bottom surface of the battery case; and

(iv) a step of injecting the nonaqueous electrolytic solution into thebattery case into which the electrode body and the insulating film areinserted.

According to this manufacturing method, a quadrilateral nonaqueouselectrolyte secondary battery can be suitably manufactured whichincludes the electrode body accommodated in the bag-shaped insulatingfilm, in which the insulating film which faces the bottom-side R portionis joined to the entire surface of the bottom-side R portion of the ofthe electrode body. That is, since the bottom-side R portion of theelectrode body and the insulating film are joined to each other beforethe electrode body is inserted into the battery case, the joining can beeasily performed. By joining the bottom-side R portion of the electrodebody and the insulating film to each other in advance, a positiondeviation of the insulating film, which may occur when the electrodebody accommodated in the insulating film is accommodated in the batterycase, can be prevented.

The insulating film may be welded to the electrode body by heating ajoint portion between the R portion of the electrode body and theinsulating film to at least 60° C. or higher while applying a pressingforce of at least 950 N to the joint portion. When the heatingtemperature and the pressing force are as described above, the electrodebody and the insulating film can be reliably joined (welded) to eachother.

The insulating film and the R portion of the electrode body may bejoined to each other through an adhesive force or a bonding force of anadhesive member or a bonding member that is arranged between theinsulating film and the electrode body. According to the manufacturingmethod, when the electrode body and the insulating film are joined toeach other, heat and pressing force applied to the electrode body andthe insulating film can be reduced. According to the manufacturingmethod, the invention is also suitably applicable to a case where theinsulating film is formed of a material which is unsuitable for welding.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the invention will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is a perspective view schematically showing the externalappearance of a nonaqueous electrolyte secondary battery according to anembodiment of the invention;

FIG. 2 is an exploded perspective view schematically showing aconfiguration of the nonaqueous electrolyte secondary battery accordingto the embodiment;

FIG. 3 is a longitudinal sectional view schematically showing asectional structure taken along line of FIG. 1;

FIG. 4 is a schematic diagram showing a configuration of a woundelectrode body according to the embodiment;

FIG. 5 is an enlarged sectional view of a sectional structure takenalong line V-V of FIG. 4, schematically showing a part of a regionbetween positive and negative electrodes of the wound electrode bodyaccording to the embodiment;

FIG. 6 is a longitudinal sectional view schematically showing alongitudinal sectional structure taken along line VI-VI of FIG. 3;

FIG. 7 is a flowchart showing a method of manufacturing the nonaqueouselectrolyte secondary battery according to the embodiment; and

FIG. 8 is a graph showing a change in resistance increase when acharging-discharging cycle test was performed on a nonaqueouselectrolyte secondary battery according to an example.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, preferred embodiments of the invention will be describedappropriately with reference to the drawings. Matters necessary toimplement the embodiments of the invention other than those specificallyreferred to in the invention may be understood as design matters basedon the related art in the pertinent field for a person of ordinary skillin the art. The invention can be practiced based on the contentsdisclosed in this description and common technical knowledge in thesubject field. In addition, in the following drawings, parts or portionshaving the same function are represented by the same reference numerals,and the repeated description thereof will not be made or will besimplified. In each drawing, a dimensional relationship (for example,length, width, or thickness) does not necessarily reflect the actualdimensional relationship.

“Secondary battery” described in this specification refers to generalstorage devices which can be repeatedly charged and discharged and is acollective term for storage elements including so-called storagebatteries such as a lithium ion secondary battery and electric doublelayer capacitors. In addition, “nonaqueous electrolyte secondarybattery” refers to batteries including a nonaqueous electrolyticsolution (typically, an electrolytic solution containing a supportingelectrolyte in a nonaqueous solvent). In addition, “lithium ionsecondary battery” refers to a secondary battery in which lithium ionsare used as charge carriers, and charging and discharging are performedby electrons moving between positive and negative electrodes along withthe lithium ions. In addition, an electrode active material refers to amaterial which can reversibly store and release chemical species(lithium ions in a lithium ion secondary battery) as charge carriers.Hereinafter, a structure of the battery according to the invention willbe described in detail using a quadrilateral lithium ion secondarybattery as an example. However, the invention is not intended to belimited to the embodiments.

In this specification, “adhesion” and “bonding” represent that twoobjects are joined to each other but are distinguished from each otherbased on whether the two objects can be peeled off from each other againafter being joined to each other. That is, “adhesion” represents thatthe two objects can be peeled off from each other again after beingjoined to each other. On the other hand, “bonding” represents that thetwo objects cannot be peeled off from each other again after beingjoined to each other.

As shown in FIGS. 1 to 3 and 6, a lithium ion secondary battery 100according to an embodiment of the invention includes a flat woundelectrode body 80, a battery case 30, and an insulating film 10.

<Battery Case 30>

As shown in FIGS. 1 to 3 and 6, the battery case 30 according to theembodiment is a so-called quadrilateral (typically, a cuboid shape)battery case having 8 corner portions in total which is formed such thatan internal space thereof has a box shape corresponding to the woundelectrode body 80. The battery case 30 includes a case body 32 and a lid34. The case body 32 has a bottomed cuboid shape and is a flatbox-shaped container having an opening on one surface (top surface). Thelid 34 is a member that is attached to the opening (upper opening) ofthe case body 32 to cover the opening. The case body 32 can accommodatethe wound electrode body 80 and the insulating film 10 through the upperopening. As shown in FIGS. 2, 3, and 6, the case body 32 includes: apair of wide side surfaces 37 that face a flat surface (flat portion) ofthe wound electrode body 80 to be accommodated in the case; a pair ofnarrow side surfaces 38 that are adjacent to the wide side surfaces 37;and a bottom surface 39. It is preferable that the battery case 30 isformed of a metal material having high strength, light weight, and highthermal conductivity. Examples of such a metal material include aluminumstainless steel, and nickel-plated steel.

The battery case 30 has a flat rectangular internal space thataccommodates the wound electrode body 80. As shown in FIGS. 2 and 3, theflat internal space of the battery case 30 has a width (length in alongitudinal direction of the wide side surfaces 37) which is slightlywider than that of the wound electrode body 80. As shown in FIGS. 1 and3, a positive electrode terminal 42 and a negative electrode terminal 44for external connection are attached to the lid 34 of the battery case30. The positive electrode terminal 42 and the negative electrodeterminal 44 penetrate the battery case 30 (lid 34) and protrude from thebattery case 30 to the outside. A thin safety valve 36, which is set torelease the internal pressure of the battery case 30, and an injectionhole (not shown), through which the nonaqueous electrolytic solution isinjected, are provided on the lid 34.

<Wound Electrode Body 80>

As shown in FIGS. 2 to 6, the wound electrode body 80 is formed bymaking an elongated positive electrode 50, an elongated negativeelectrode 60 overlap each other with two elongated separators 70 toobtain a laminate and winding the laminate into a flat shape in alongitudinal direction of the elongated positive and negativeelectrodes. That is, as shown in the drawings, the flat wound electrodebody 80 has two R portions 80R1, 80R2 and a wide flat portion 80F, thetwo R portions have a curved surface and are formed in opposite endportions in a longitudinal direction of a section perpendicular to awinding axis WL, and the wide flat portion is a center portion in thelongitudinal direction of the section and is interposed between the twoR portions. As shown in FIGS. 2, 3, and 6, the wound electrode body 80is accommodated in the battery case 30 (that is, the case body 32) suchthat the longitudinal direction of the section perpendicular to thewinding axis WL is a vertical direction of the battery case (in aposture in which the winding axis WL of the wound electrode body 80 liessideways that is, the opening of the case body 32 is formed in thenormal direction of the winding axis WL of the wound electrode body 80)and such that the R portion 80R1 of the two R portions 80R1, 80R2 facesthe bottom surface 39 of the battery case. Hereinafter, the R portion80R1 of the wound electrode body which faces the bottom surface 39 ofthe battery case will also referred to as “lower R portion”. The lower Rportion can be regarded as “bottom-side R portion” of the presentinvention.

The positive electrode 50, the negative electrode 60, and the separators70 are elongated (belt-shaped) sheet members, respectively. In thepositive electrode 50, a positive electrode active material layer 54 isformed on a single surface or both surfaces (herein, both surfaces) ofan elongated (belt-shaped) positive electrode current collector 52 inthe longitudinal direction. On one end portion of the positive electrodecurrent collector 52 in a width direction, a portion where the positiveelectrode current collector 52 is exposed without the positive electrodeactive material layer 54 being formed in a belt shape along the endportion (that is, a positive electrode active material layer non-formingportion 53) is formed. In the negative electrode 60, a negativeelectrode active material layer 64 is formed on a single surface or bothsurfaces (herein, both surfaces) of an elongated negative electrodecurrent collector 62 in the longitudinal direction. On one end portionof the negative electrode current collector 62 in a width direction, aportion where the negative electrode current collector 62 is exposedwithout the negative electrode active material layer 64 being formed ina belt shape along the end portion (that is, a negative electrode activematerial layer non-forming portion 63) is formed.

In the embodiment as shown in FIGS. 4 and 5, the respective activematerial layers are formed such that a width b1 of the negativeelectrode active material layer 64 is slightly wider than a width a1 ofthe positive electrode active material layer 54. Further, a width c1 ofthe separators 70 is slightly wider than the width b1 of the negativeelectrode active material layer 64 (c1>b1>a1). The positive electrode50, the negative electrode 60, and the separators 70 are aligned in thelongitudinal direction so as to overlap each other in the followingorder: the positive electrode 50, the separator 70, the negativeelectrode 60, and the separator 70. The positive electrode activematerial layer non-forming portion 53 of the positive electrode 50 andthe negative electrode active material layer non-forming portion 63 ofthe negative electrode 60 protrude to opposite sides in the widthdirection of the separator 70. The positive electrode 50, the negativeelectrode 60, and the separators 70 which overlap each other are woundaround the winding axis WL set in the width direction. In theembodiment, the positive electrode 50, the negative electrode 60, andthe two separators 70 are made to overlap each other, thereby formingthe flat wound electrode body 80. As a result, at the center of thewound electrode body 80 in the winding axial direction, the laminate(winding core portion) is formed in which the positive electrode 50, thenegative electrode 60, and the separators 70 are laminated and wound.

As shown in FIGS. 2 and 3, the positive electrode active material layernon-forming portion 53 and the negative electrode active material layernon-forming portion 63, which protrude from the winding core portion ofthe wound electrode body 80, are joined to a positive electrode currentcollector plate 42 a and a negative electrode current collector plate 44a, respectively, so as to be electrically connected to the positiveelectrode terminal 42 and the negative electrode terminal 44. Thepositive electrode current collector plate 42 a is formed of, forexample, aluminum or an aluminum alloy. In this example, as shown inFIG. 3, the positive electrode current collector plate 42 a extends tothe center of the positive electrode active material layer non-formingportion 53 of the wound electrode body 80. A tip end portion of thepositive electrode current collector plate 42 a is joined (here, iswelded) to the center of the positive electrode active material layernon-forming portion 53. The negative electrode current collector plate44 a is formed of, for example, copper or a copper alloy. In thisexample, as shown in FIG. 3, the negative electrode current collectorplate 44 a extends to the center of the negative electrode activematerial layer non-forming portion 63 of the wound electrode body 80. Atip end portion of the negative electrode current collector plate 44 ais joined (here, is welded) to the center of the negative electrodeactive material layer non-forming portion 63.

<Insulating Film 10>

The insulating film 10 is arranged between the wound electrode body 80and the battery case 30 so as to separate the wound electrode body 80and the battery case 30 from each other. Due to this insulating film 10,direct contact between the wound electrode body 80, which is a powergenerating element, and the battery case 30 can be avoided, andinsulation between the wound electrode body 80 and the battery case 30can be secured. The insulating film 10 may be formed of any materialwhich can function as an insulating member. Typically, it is preferablethat the insulating film 10 is formed of a flexible material which canbe curved along the shape of the R portion of the wound electrode body80. For example, a resin material such as polypropylene (PP) orpolyethylene (PE) can be preferably used. An insulating film formed of athermoplastic resin can be preferably used, in particular, when thewound electrode body 80 and the insulating film are joined to each otherthrough welding.

The average thickness of the insulating film 10 may be about 100 μm butcan be appropriately changed depending on, for example, constructionconditions of the battery 100. For example, the average thickness of theinsulating film 10 is 20 μm or more (preferably, 50 μm or more) and 200μm or less (preferably, 100 μm or less). It is preferable that thethickness of the insulating film 10 is small because the space of theinsulating film 10 in the battery case 30 can be minimized when theinsulating film 10 is accommodated in the battery case 30 together withthe wound electrode body 80. On the other hand, when the thickness ofthe insulating film is excessively small, the durability of theinsulating film may deteriorate, and it may be difficult to secure theinsulation between the electrode body 80 and the battery case. Theinsulating film 10 may have a single-layer structure or a laminatestructure including two or more layers within a range where the effectsof the invention can be exhibited.

Here, as shown in FIGS. 2, 3, and 6, the insulating film 10 may beformed in a bag shape surrounding the wound electrode body 80.Specifically, the insulating film 10 is formed in a bag shapecorresponding to the shape of the wound electrode body 80. Theinsulating film 10 has a bottomed bag shape having an opening at anupper end, and the wound electrode body 80 can be accommodated in theinsulating film 10 through the opening.

As shown in FIGS. 2, 3, and 6, roughly, the bag-shaped insulating film10 includes: wide side surface-forming portions that form a pair of wideside surfaces facing the wide side surfaces 37 of the battery case 30(case body 32) (the flat portion 80F of the wound electrode body 80facing the wide side surfaces); a bottom surface-forming portion that ispresent between the pair of wide side surface-forming portions and formsa bottom surface of the insulating film 10 facing the bottom surface 39of the battery case 30 (case body 32) (the R portion 80R1 of the woundelectrode body 80 facing the bottom surface 39, that is, the lower Rportion); and narrow side surface-forming portions that are present onopposite sides of the pair of wide side surface-forming portions,respectively, and form a pair of narrow side surfaces facing the narrowside surfaces 38 of the battery case 30 (the case body 32).

The shape of the bottom surface-forming portion (that is, the portionfacing the lower R portion of the wound electrode body 80) of thebag-shaped insulating film 10 is not particularly limited and, forexample, may be a U-shape, a V-shape, or an inverted C shape. It ispreferable that the bottom surface-forming portion (that is, the portionfacing the lower R portion of the wound electrode body 80) of theinsulating film 10 is bent to have a gently curved shape (U-shape)obtained as shown in FIGS. 2 and 6. It is more preferable that thebottom surface-forming portion has a shape corresponding to (preferably,similar to) the shape of the lower R portion 80R1 of the wound electrodebody 80. By forming the shape of the bottom surface-forming portion(that is, the portion facing the lower R portion of the wound electrodebody 80) of the bag-shaped insulating film 10 into the above-describedshape, the area of a gap which may be formed between the lower R portionof the wound electrode body 80 and the insulating film 10 facing thelower R portion can be minimized By forming the shape of the bottomsurface-forming portion (that is, the portion facing the lower R portionof the wound electrode body 80) of the bag-shaped insulating film intothe above-described U-shape (curved shape), the corrugation or twistingof the insulating film 10 can be prevented when the entire surface ofthe lower R portion of the wound electrode body 80 and the insulatingfilm 10 (typically, the portion facing the lower R portion of the woundelectrode body 80) are joined to each other.

The bag-shaped insulating film 10 can be formed, for example, by foldingthe insulating film, which has been cut into a predetermined shape, intothe above-described shape and assembling the folded insulating film intoa bag shape. At this time, for example, the insulating film is cut intoa shape (typically, an exploded shape of the bag-shaped insulating film)where portions (typically, portions of the narrow side surface-formingportions) of the insulating film overlap each other when being assembledinto a bag shape, and the overlapping portions are bonded (fixed) toeach other. As a result, the insulating film can be formed into a bagshape. Alternatively, plural sheets (parts) may be combined (bonded) toeach other to be formed in the above-described bag shape. When theportions of the insulating film are bonded to each other, welding meanssuch as spot welding, heat welding, ultrasonic welding, or laser weldingcan be appropriately used. Alternatively, the portions of the insulatingfilm may be fixed to each other through, for example, an adhesive or abonding agent as long as they can be sufficiently fixed to each otherand there are no adverse effects (for example, internalshort-circuiting) on battery performance. Here, typically, portionswhich are bonded (fixed) to each other during the formation of theinsulating film 10 are liquid-tightly bonded to each other, and thus nothrough-hole is present in the bottom surface-forming portion of theinsulating film 10. It is preferable that the bag-shaped insulating film10 has a shape in which no through-hole is present in any region otherthan the upper opening. In other words, it is preferable that thebag-shaped insulating film 10 is formed such that the nonaqueouselectrolytic solution in the bag-shaped insulating film does not flowout (leak) from the bonded portions of the insulating film and/or thebottom surface-forming portion of the insulating film to the outside. Byforming the insulating film 10 into the above-described shape, theperformance of holding the nonaqueous electrolytic solution in theelectrode body can be further improved. Typically, it is preferable thatthe insulating film is formed such that the nonaqueous electrolyticsolution injected into the bag-shaped insulating film does not flow out(leak) from the regions of the bag-shaped insulating film 10 other thanthe upper opening to the outside.

The inside (surface facing the wound electrode body) of the bottomsurface-forming portion of the bag-shaped insulating film 10 is joinedto the entire surface of the lower R portion 80R1 of the wound electrodebody 80. That is, the entire surface of the lower R portion 80R1 of thewound electrode body 80 and the inside of the bag-shaped insulating filmfacing the lower R portion of the electrode body are joined to eachother. Here, joining represents that the wound electrode body 80 and theinsulating film 10 are coupled with each other so as not to be separatedfrom each other and includes joining using welding (also called fusing)and joining using an adhesive or a bonding agent.

Here, the materials and members constituting the wound electrode body 80(for example, the materials and members constituting the positiveelectrode 50, the negative electrode 60, and the separators 70) and thenonaqueous electrolytic solution may have the same configurations as ina nonaqueous electrolyte secondary battery (lithium ion secondarybattery) of the related art without any particular limitation. A typicalconfiguration will be described below.

<Positive Electrode 50>

The positive electrode 50 of the lithium ion secondary battery(nonaqueous electrolyte secondary battery) 100 according to theembodiment includes the positive electrode current collector 52; and thepositive electrode active material layer 54 that is formed on thepositive electrode current collector 52. As a material of the positiveelectrode current collector 52, a conductive material formed of highlyconductive metal can be preferably used as in the case of a positiveelectrode current collector for a nonaqueous electrolyte secondarybattery of the related art. For example, aluminum, nickel, titanium, orstainless steel, or an alloy containing the metal as a major componentcan be used. Among these, aluminum foil or the like is preferable. Thepositive electrode active material layer 54 contains at least a positiveelectrode active material. Preferable examples of the positive electrodeactive material include lithium composite metal oxides having a crystalstructure such as a layered structure or a spinel structure (forexample, LiNi_(1/3)CO_(1/3)Mn_(1/3)O₂, LiNiO₂, LiCoO₂, LiFeO₂, LiMn₂O₄,LiNi_(0.5)Mn₁₅O₄, and LiFePO₄). The positive electrode active materiallayer 54 may further contain components other than the positiveelectrode active material, for example, a conductive material or abinder. As the conductive material, for example, a carbon material suchas carbon black (for example, acetylene black (AB)) or graphite may bepreferably used. As the binder, for example, PVDF may be used.

First, the positive electrode active material and other optionalmaterials are dispersed in an appropriate solvent (for example,N-methyl-2-pyrrolidone) to prepare a paste-like (slurry-like)composition. Next, an appropriate amount of the composition is appliedto a surface of the positive electrode current collector 52 and then isdried. As a result, the positive electrode 50 can be formed. Inaddition, by optionally performing an appropriate pressing treatment,the characteristics (for example, average thickness, density, andporosity) of the positive electrode active material layer 54 can beadjusted.

<Negative Electrode 60>

The negative electrode 60 of the lithium ion secondary battery(nonaqueous electrolyte secondary battery) 100 according to theembodiment includes the negative electrode current collector 62; and thenegative electrode active material layer 64 that is formed on thenegative electrode current collector 62. As a material of the negativeelectrode current collector 62 constituting the negative electrode 60, aconductive material formed of highly conductive metal can be preferablyused as in a current collector of a negative electrode for a nonaqueouselectrolyte secondary battery of the related art. For example, copper,nickel, titanium, or stainless steel, or an alloy containing the metalas a major component can be used. Among these, copper foil or the likeis preferable. The negative electrode active material layer 64 containsat least a negative electrode active material. As the negative electrodeactive material, one kind or two or more kinds may be used without anyparticular limitation among various known materials which can be used asa negative electrode active material of a nonaqueous electrolytesecondary battery. For example, a particulate carbon material (carbonparticles) at least a part of which has a graphite structure (layeredstructure) can be preferably used. As the carbon material, graphite, anyone of non-graphitizable carbon (hard carbon), graphitizable carbon(soft carbon), and a carbon material having a combination thereof can bepreferably used. Among these, graphite particles (formed of naturalgraphite or artificial graphite) capable of obtaining high energydensity can be preferably used. In addition, a surface of the carbonmaterial (carbon material as a core) may be coated with an amorphouscarbon film.

The negative electrode 60 can be manufactured, for example, using thesame method as in the positive electrode 50. That is, the negativeelectrode active material and other optional materials are dispersed inan appropriate solvent (for example, ion exchange water) to prepare apaste-like (slurry-like) composition. Next, an appropriate amount of thecomposition is applied to a surface of the negative electrode currentcollector 62 and then is dried to remove the solvent. As a result, thenegative electrode 60 can be formed. In addition, by optionallyperforming an appropriate pressing treatment, the characteristics (forexample, average thickness, density, and porosity) of the negativeelectrode active material layer 64 can be adjusted.

<Separator 70>

The separator 70 has a function of insulating the positive electrode 50(positive electrode active material layer 54) and the negative electrode60 (negative electrode active material layer 64) from each other, afunction of holding the nonaqueous electrolytic solution, and a shutdownfunction. Examples of the separator 70 include a porous sheet (film)formed of a resin such as polyethylene (PE), polypropylene (PP),polyester, cellulose, or polyamide. The porous sheet may have asingle-layer structure or a laminate structure including two or morelayers (for example, a three-layer structure in which a PP layer islaminated on both surfaces of a PE layer).

In the nonaqueous electrolytic solution, for example, an organic solvent(nonaqueous solvent) can contain a supporting electrolyte. As thenonaqueous solvent, various organic solvents used in an electrolyticsolution of a general lithium ion secondary battery, for example,ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate(DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) can beused without any particular limitation. Among these nonaqueous solvents,one kind can be used alone, or two or more kinds can be appropriatelyused in combination. In particular, a nonaqueous solvent which containsEC having a high dielectric constant can be preferably used. As thesupporting electrolyte, for example, a lithium salt such as LiPF₆,LiBF₄, or LiClO₄ (preferably, LiPF₆) can be used. The concentration ofthe supporting electrolyte is preferably 0.7 mol/L to 1.3 mol/L and ismore preferably about 1.1 mol/L. Within a range where the effects of theinvention do not significantly deteriorate, the nonaqueous electrolyticsolution may further contain components other than the nonaqueoussolvent and the supporting electrolyte described above. Examples of thecomponents include various additives including: a gas producing agentsuch as biphenyl (BP) or cyclohexylbenzene (CHB); a film forming agentsuch as an oxalato complex compound, vinylene carbonate (VC), orfluoroethylene carbonate (FEC); a dispersant; and a thickener.

Hereinafter, in regard to a method of manufacturing a nonaqueouselectrolyte secondary battery according to the invention, a preferableembodiment of a method of manufacturing the nonaqueous electrolytesecondary battery (lithium ion secondary battery) 100 having theabove-described configuration will be described appropriately withreference to the drawings. However, the method of manufacturing anonaqueous electrolyte secondary battery according to the invention isnot intended to be limited to the following embodiment.

As shown in FIG. 7, the method of manufacturing the nonaqueouselectrolyte secondary battery 100 according to the embodiment includes awound electrode body construction step S10, a joining step S20, anaccommodating step S30 of accommodating the electrode body in thebattery case, a nonaqueous electrolytic solution injection step S40.Hereinafter, the respective steps will be described in detail.

First, the wound electrode body construction step S10 will be described.In this step, the flat wound electrode body 80 is constructed by makingthe elongated positive electrode 50 and the elongated negative electrode60 overlap each other with the elongated separator 70 interposedtherebetween to obtain a laminate and winding the laminate in alongitudinal direction of the elongated positive electrode and theelongated negative electrode. The wound electrode body 80 has two Rportions 80R1, 80R2 and a wide flat portion (80F), the two R portionshave a curved surface and are formed in opposite end portions in alongitudinal direction of a section perpendicular to a winding axis, andthe wide flat portion is a center portion in the longitudinal directionof the cross-section and is interposed between the two R portions.

The flat wound electrode body 80 may have the above-describedconfiguration. The wound electrode body 80 can be formed into a flatshape, for example, by making the positive and negative electrodes andthe separators overlap each other to obtain a laminate, winding thelaminate to obtain a wound body, and squashing the wound body in a sidesurface direction (in a direction perpendicular to the winding axis WL).Alternatively, the wound electrode body 80 may be formed into a flatshape by making the positive and negative electrodes and the separatoroverlap each other to obtain a laminate and winding the laminate arounda flat winding core.

Next, the joining step S20 will be described. In this step, the flatwound electrode body 80 constructed in the wound electrode bodyconstruction step S10 is accommodated in the bag-shaped insulating film10, and an entire surface of one (R portion 80R1) of the two R portions80R1, 80R2 of the wound electrode body 80 and an inside of thebag-shaped insulating film 10, which faces the R portion 80R1 of theelectrode body 80, are joined to each other.

The wound electrode body 80 is accommodated in the bag-shaped insulatingfilm 10 such that the flat portion 80F of the wound electrode body 80faces the wide side surfaces of the insulating film 10 and such that theR portion 80R1 (the R portion which faces the bottom surface 39 of thebattery case when accommodated in the battery case, that is, the lower Rportion) of the wound electrode body faces the bottom surface-formingportion of the insulating film 10. As a method of accommodating thewound electrode body 80 in the bag-shaped insulating film 10 (coveringthe wound electrode body 80 with the insulating film 10), for example,the following method can be adopted including: forming the insulatingfilm 10 into a bag shape corresponding to the shape of the woundelectrode body 80; and inserting the wound electrode body 80 into thebag-shaped insulating film 10. At this time, the wound electrode body 80can be inserted into the bag-shaped insulating film through the openingwhich is formed at an end of the bag-shaped insulating film 10.Alternatively, the wound electrode body 80 may be arranged at apredetermined position of the insulating film 10 which has been cut intoa predetermined shape, and the insulating film 10 may be assembled(formed) into a bag shape in a state where the wound electrode body 80is arranged. In the method of forming the insulating film into a bagshape after arranging the wound electrode body at a predeterminedposition, an operation of inserting the wound electrode body 80 into theflat bag-shaped insulating film 10 is not required. Therefore, forexample, the insulating film 10 may not be damaged (broken or torn) bythe wound electrode body 80.

The method of joining the entire surface of the R portion 80R1 of thetwo R portions 80R1, 80R2 of the wound electrode body 80 and the insideof the bag-shaped insulating film 10, which faces the R portion 80R1, toeach other is not particularly limited as long as the wound electrodebody 80 and the insulating film 10 can be joined to each other usingthis method. For example, joining using welding and joining using anadhesive force of an adhesive or a bonding force of a bonding agent canbe preferably adopted.

The joining using welding refers to a method of pressing the molteninsulating film 10 against the wound electrode body 80 to join them toeach other. For example, the joining using welding is performed byheating the insulating film 10 while applying a pressing force to theinsulating film 10 such that the portion of the insulating film 10 whichis joined to the R portion 80R1 of the wound electrode body 80 (theinside of the bag-shaped insulating film 10 which faces the R portion80R1 of the wound electrode body 80, that is, the portion of the bottomsurface-forming portion of the insulating film 10 which faces the woundelectrode body) is closely adhered to the wound electrode body 80.Although not particularly limited, the wound electrode body 80 and theinsulating film 10 can be joined to each other, for example, using thefollowing means. First, a pressing tool having a curved surface whichcorresponds to the shape of the R portion 80R1 of the wound electrodebody 80 is prepared, and the insulating film 10 is arranged between thecurved surface of the pressing tool and the R portion 80R1 of the woundelectrode body 80. The pressing tool is pressed against the woundelectrode body 80 at a predetermined pressing force in a direction whichmatches the longitudinal direction of the section perpendicular to thewinding axis of the wound electrode body 80. As a result, the R portion80R1 of the wound electrode body 80 and the insulating film 10(typically, the bottom surface-forming portion of the insulating film10) are closely adhered to each other. The insulating film 10 is heatedto a predetermined temperature while maintaining a state where theinsulating film 10 is pressed against the wound electrode body 80 usingthe pressing tool. As the welding method, a well-known welding method ofthe related art can be adopted without any particular limitation, andexamples thereof include thermal welding (for example, hot plate weldingor impulse welding), vibration welding, high-frequency welding, andultrasonic welding.

When the wound electrode body 80 and the insulating film 10 are joinedto each other through welding, the pressing force at which theinsulating film 10 is pressed against the wound electrode body 80 is notparticularly limited as long as the joining between the wound electrodebody 80 and the insulating film 10 can be realized. For example,although it varies depending on, for example, the material of theinsulating film 10 to be used, the pressing force is suitably about 100kgf or higher (for example, 100 kgf to 500 kgf) and preferably 150 kgfor higher (for example, 150 kgf to 300 kgf). When the pressing force isexcessively low, it is difficult to join the wound electrode body 80 andthe insulating film 10 to each other, and when the pressing force isexcessively high, the wound electrode body 80 may be damaged, which isnot preferable. Here, 1 kgf refers to about 9.8 N. The preferable rangeof the pressing force is suitably about 950 N or higher (for example,950 N to 5000 N) and is preferably 1400 N or higher (for example, 1400 Nto 3000 N). When the wound electrode body 80 and the insulating film 10are joined to each other through welding, the heating temperature of theinsulating film 10 is not particularly limited as long as the joiningbetween the wound electrode body 80 and the insulating film 10 can berealized. For example, the heating temperature may be about 60° C. orhigher, and the heating time may be at least 0.1 seconds. Although theheating temperature and the heating time vary depending on, for example,the material of the insulating film 10 to be used, the heatingtemperature is suitably about 60° C. or higher (for example, 60° C. to130° C.) and preferably 100° C. to 110° C. The heating time is suitablyabout 0.1 seconds or longer (for example, 0.1 seconds to 10 seconds) andpreferably 0.5 seconds to 8 seconds (for example, 1 second to 5seconds). When the pressing force, the heating temperature, and theheating time are within the above-described range, the insulating film10 and the wound electrode body 80 can be appropriately joined to eachother. When the heating temperature is excessively high or when theheating time is excessively long, the performance of the materialconstituting the electrode body may decrease (for example, the separatormay be melted). On the other hand, when the heating temperature isexcessively low or when the heating time is excessively short, thejoining between the wound electrode body 80 and the insulating film 10may be insufficient, which is not preferable.

As the adhesive or the bonding agent through which the wound electrodebody 80 and the insulating film 10 are joined to each other, awell-known adhesive or a well-known bonding agent of the related art canbe used without any particular limitation as long as the batteryperformance of the nonaqueous electrolyte secondary batterysignificantly deteriorates. For example, the adhesive or the bondingagent may be in various forms such as liquid, ink, paste, and slurry. Itis preferable that the adhesive or the bonding agent is in the form of atape (typically, a double-sided adhesive tape). In the embodiment of theinvention, both the adhesive and the bonding agent can be preferablyused, particularly, without being distinguished from each other. In amethod of joining the wound electrode body 80 and the insulating film 10to each other using the adhesive or the bonding agent, for example, theadhesive or the bonding agent is applied (for example, is coated or ispasted) to the surface of the R portion 80R1 of the wound electrode body80 or to the surface of the region where the insulating film 10 isjoined to the R portion 80R1 of the wound electrode body 80 (that is,the surface of the bottom surface-forming portion of the insulating film10 which faces the wound electrode body), and the R portion 80R1 of thewound electrode body 80 and the insulating film 10 come into contactwith each other. As a result, the wound electrode body 80 and theinsulating film 10 can be joined to each other. Alternatively, when ahot-melt type adhesive or bonding agent is used, the wound electrodebody 80 and the insulating film 10 may be joined to each other forexample, by arranging the hot-melt type adhesive or bonding agentbetween the R portion 80R1 of the wound electrode body 80 and theinsulating film 10, putting the wound electrode body 80 and theinsulating film 10 into a mold having a shape corresponding to the shapeof the R portion 80R1 of the wound electrode body, and heating the mold.

Next, the step S30 of accommodating the electrode body in the batterycase will be described. In this step, the wound electrode body 80 towhich the insulating film 10 is joined is inserted into the battery case30. Specifically, the wound electrode body 80 and the insulating film 10are inserted into the battery case 30 (case body 32) such that the Rportion 80R1 of the two R portions 80R1, 80R2 of the flat woundelectrode body 80, to which the insulating film 10 is joined, faces thebottom surface 39 of the battery case 30. The wound electrode body 80and the insulating film are accommodated in the battery case 30 throughthe opening provided on the upper portion of the case body 32. As aresult, the wound electrode body 80 and the insulating film 10 areaccommodated in the flat internal space of the case body 32, and theinsulating film 10 is arranged between the wound electrode body 80 andthe inner wall of the battery case 30 (case body 32). After theinsulating film 10 and the wound electrode body 80 are accommodated inthe case body 32, the upper opening of the case body 32 is covered withthe lid 34, a boundary between the case body 32 and the lid 34 is joined(sealed), for example, by welding (for example, by laser welding) thelid 34 to the periphery of the opening of the case body 32.

Next, the nonaqueous electrolytic solution injection step S40 will bedescribed. In this step, the nonaqueous electrolytic solution isinjected into the battery case 30 into which the wound electrode body 80and the insulating film 10 are inserted. For example, the nonaqueouselectrolytic solution may be injected into the battery case 30 throughthe injection hole provided on the lid 34 of the battery case. As theinjecting method, a general injecting method of injecting the nonaqueouselectrolytic solution into the battery case 30 during the preparation ofa nonaqueous electrolyte secondary battery of the related art can beadopted. The nonaqueous electrolytic solution may have theabove-described configuration. Typically, after the nonaqueouselectrolytic solution is injected into the battery case 30, the liquidinjection hole is sealed. The sealing can be performed, for example, bycaulking the injection hole with a sealing plug and welding (forexample, laser welding) the sealing plug to the injection hole. In thisway, the lithium ion secondary battery 100 can be manufactured(constructed).

The nonaqueous electrolyte secondary battery according to the embodimentcan be used for various applications and is characterized in that it issuperior in the ability of holding the nonaqueous electrolytic solutionin the electrode body and exhibits high cycle characteristics (inparticular, high-rate cycle characteristics). That is, batterycharacteristics (typically, capacity retention) are high, andreliability is high. Accordingly, due to its characteristics, thenonaqueous electrolyte secondary battery according to the embodiment canbe preferably used, for example, as a drive power supply mounted in avehicle such as a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV),or an electric vehicle (EV). According to the invention, there can beprovided a vehicle including the nonaqueous electrolyte secondarybattery disclosed herein, preferably, as a power source (typically, abattery pack in which plural secondary batteries are electricallyconnected to each other).

Hereinafter, test examples relating to the invention will be described.However, the descriptions of these test examples are not intended tolimit the technical scope of the invention.

Using the following materials and processes, lithium ion secondarybatteries (nonaqueous electrolyte secondary batteries) according toExample 1 (Example according to the invention) and Example 2(Comparative Example) were constructed.

Example 1

The positive electrode was prepared in the following procedure.LiNi_(0.33)Co_(0.33)Mn_(0.33)O₂ (LNCM) as a positive electrode activematerial; AB as a conductive material; and PVDF as a binder were weighedat a mass ratio (LNCM:AB:PVDF) of 91:6:3. These weighed materials weremixed with N-methylpyrrolidone (NMP) to prepare a positive electrodeactive material layer-forming composition. This composition was appliedin a belt shape to both surfaces of elongated aluminum foil (positiveelectrode current collector) was dried, and was pressed. As a result, apositive electrode was prepared.

The negative electrode was prepared in the following procedure. Graphite(C) as a negative electrode active material; SBR as a binder; and CMC asa thickener were weighed at a mass ratio (C:SBR:CMC) of 98:1:1. Theweighed materials were mixed with ion exchange water. As a result, anegative electrode active material layer-forming composition wasprepared. This composition was applied in a belt shape to both surfacesof elongated copper foil (negative electrode current collector), wasdried, and was pressed. As a result, a negative electrode sheet wasprepared.

The positive electrode and the negative electrode which were preparedusing the above-described method were made to overlap each other in alongitudinal direction with two separators interposed therebetween, eachof the separators having a three-layer structure in which a porouspolypropylene layer was formed on both surfaces of a porous polyethylenelayer. Next, the obtained laminate was wound in the longitudinaldirection and then squashed. As a result, a flat wound electrode bodywas prepared.

Next, a bag-shaped insulating film was prepared which was formed into abag shape corresponding to the shape of the flat wound electrode bodyprepared as described above. The bag-shaped insulating film was formed,for example, by folding the insulating film, which had been cut into apredetermined shape, into a predetermined shape and fixing a part ofoverlapping narrow side surface-forming portions by heat welding toassemble the insulating film into a bag shape. As the insulating film, afilm formed of a thermoplastic resin having an average thickness of 50μm was used.

The flat wound electrode body prepared as described was accommodated inthe bag-shaped insulating film prepared as described above.Specifically, the electrode body was inserted into the insulating filmthrough an opening of the insulating film such that one of R portions ofthe wound electrode body faced a bottom surface-forming portion of theinsulating film.

Next, regarding the wound electrode body accommodated in the bag-shapedinsulating film, the entire surface of the R portion (the R portionwhich faces the bottom surface-forming portion of the bag-shapedinsulating film; lower R portion) of the two R portions and the insideof the insulating film (the bottom surface-forming portion of theinsulating film) facing the R portion (lower R portion) of the electrodebody were joined to each other. Here, a joint portion between the Rportion (lower R portion) of the electrode body and the insulating filmwas heated to about 60° C. while applying a pressing force of about 100kgf to the joint portion. As a result, the inside of the bag-shapedinsulating film was welded to the electrode body, and the electrode body(the lower R portion of the wound electrode body) and the insulatingfilm were joined to each other.

The wound electrode body to which the insulating film was joined asdescribed above was accommodated in the battery case. Here, theelectrode body and the insulating film were inserted into the batterycase through the opening of the battery case such that the R portion(lower R portion) of the two R portions of the electrode body, to whichthe insulating film was joined, faced a bottom surface of the batterycase. Next, a nonaqueous electrolytic solution was injected into thebattery case in which the wound electrode body was accommodated. As aresult, a battery according to Example 1 was constructed. As thenonaqueous electrolytic solution, a solution was used in which LiPF₆ asa supporting electrolyte was dissolved in a mixed solvent at aconcentration of 1.1 mol/L, the mixed solvent containing ethylenecarbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate(EMC) at a volume ratio (EC:DMC:EMC) of 30:40:30.

Example 2

A nonaqueous electrolyte secondary battery according to Example 2(Comparative Example) was prepared using the same material and processas in Example 1, except that the R portion (lower R portion) of thewound electrode body and the insulating film facing the R portion (lowerR portion) were not joined to each other.

[Measurement of Initial Resistance (IV Resistance)]

Next, the initial resistance (IV resistance) of each of the batteriesprepared as described above was measured. First, CC charging wasperformed until the state of charge (SOC) reached 60%. Next, in atemperature condition of −10° C., CC charging was performed on each ofthe batteries with the adjusted SOC of 60% at a charging rate of 10 Cfor 10 seconds. At this time, a value (V) of voltage increase wasmeasured. The measured value (V) of voltage increase was divided by thecorresponding current value to calculate an IV resistance (mΩ),(typically, the IV resistance (mΩ) was calculated from a slope of alinear approximation line of a current (I)-voltage (V) plot value), andthe average thereof was obtained as an initial resistance.

[Charging-Discharging Cycle Test]

After the initial IV resistance was measured, the followingcharging-discharging cycle test was performed on each of the batteriesaccording to the examples. After the test, the IV resistance wasmeasured to evaluate durability. Specifically, CC charging was performedat a charging rate of 35 C for 10 seconds, and then this chargingoperation was stopped for 5 seconds. Next, CC discharging was performedat a discharging rate of 35 C for 10 seconds, and then this dischargingoperation was stopped for 5 seconds. These charging and dischargingoperations were set as one cycle and were repeated. The resistance ofeach of the batteries was measured using the same method as in theinitial resistance measurement per 100 charging-discharging cycles.Based on the results, a resistance increase was calculated from thefollowing expression

Resistance Increase (%)=Battery Resistance (IV Resistance) afterCycles÷Initial Resistance (IV resistance)×100

FIG. 8 shows a graph in which a resistance increase (%) of each of thebatteries according to the examples was plotted per 100 cycles.

As shown in FIG. 8, in the nonaqueous electrolyte secondary batteryaccording to Example 1 (Example according to the invention), an increasein resistance caused by repeated charging and discharging was suppressedcompared to the nonaqueous electrolyte secondary battery according toExample 2 (Comparative Example). That is, regarding the nonaqueouselectrolyte secondary battery in which the flat wound electrode bodyaccommodated in the insulating film and the nonaqueous electrolyticsolution were accommodated in the battery case, it was found that thedurability of the battery (typically, cycle characteristics;specifically, high-rate cycle characteristics) can be improved byjoining the entire surface of the lower R portion of the wound electrodebody and the inside of the bag-shaped insulating film facing the lower Rportion of the electrode body. The reason for this is presumed to be asfollows: by accommodating the flat wound electrode body in thebag-shaped insulating film and joining the entire surface of the lower Rportion of the wound electrode body and the inside of the bag-shapedinsulating film, facing the lower R portion of the electrode body, toeach other, the ability of holding the nonaqueous electrolytic solutionin the electrode body can be improved, and an appropriate amount of thenonaqueous electrolytic solution can be held in the electrode body evenwhen charging and discharging were repeated. It can be seen from theresults that, according to the technique disclosed herein, a nonaqueouselectrolyte secondary battery having high ability of holding thenonaqueous electrolytic solution in the electrode body, and a method ofmanufacturing the battery can be provided.

Hereinabove, specific examples of the invention have been described indetail. However, these examples are merely exemplary and do not limitthe invention. The invention includes various modifications andalternations of the above-described specific examples.

What is claimed is:
 1. A nonaqueous electrolyte secondary batterycomprising: a flat wound electrode body that is formed by making anelongated positive electrode and an elongated negative electrode overlapeach other with an elongated separator interposed therebetween to obtaina laminate and winding the laminate in a longitudinal direction of theelongated positive electrode and the elongated negative electrode, inwhich the flat wound electrode body has two R portions and a flatportion, the two R portions have a curved surface and are formed inopposite end portions in a longitudinal direction of a sectionperpendicular to a winding axis, and the flat portion is a centerportion in the longitudinal direction of the section and is interposedbetween the two R portions; a nonaqueous electrolytic solution; aquadrilateral battery case that accommodates the flat wound electrodebody and the nonaqueous electrolytic solution; and an insulating filmthat electrically insulates the flat wound electrode body and thequadrilateral battery case from each other, is formed into a bag shapecorresponding to a shape of the flat wound electrode body, and isarranged between an inner wall of the quadrilateral battery case and theflat wound electrode body such that an entire surface of a bottom-side Rportion of the two R portions of the flat wound electrode body, whichfaces a bottom surface of the quadrilateral battery case, and an insideof the bag-shaped insulating film, which faces the bottom-side R portionof the two R portions of the flat wound electrode body, are joined toeach other, wherein the entire surface of the bottom-side R portion ofthe two P portions of the flat wound electrode body and the inside ofthe bag-shaped insulating film which faces the bottom-side R portion ofthe two R portions of the flat wound electrode body are joined to eachother through an adhesive member or a bonding member.